Mass spectrometer



April 24, 1956 LH. MCLAREN ET AL 2,743,370

MASS sPEcTRoMETER Filed Nov. 26, 1952 2 Sheets-Sheet l MRW April 24,1956 l. H. MCLAREN ET A1.

MASS SPECTROMETER 2 Sheets-Sheet 2 Filed NOV. 26, 1952 mlm] JNVENToRs/A/v M MCM/mv By w/LL/AM c. W/y

MRM

United States PatentO l This invention relates to mass spectrometersand, more particularly, to mass spectrometers for operating in asimple/manner to determine the masses of different ionsv byrmeasuringthe time required 4for the ions to travel through a predetermineddistance. The invention also relates to methods of determining themasses of different ions.

In some types of mass spectrometers, pulses of ions are utilized todetermine the masses of the Vdilferent gases or vapors in an unknownmixture and the relative abundance of the gases and vapors in themixture. The pulses of ions are accelerated by a force for movementthrough a predetermined distance. Because of this force, the ions ofrelatively light mass attain a greatervelocity than the ions of heavymass and travel through the predetermined distance before the ions ofheavy mass. By indicating the relative times at which the ions ofdifferent mass travel through the predetermined clistance, the -massesof the ions can be determined.

Until now, pulses of ions have been formed by the application of pulsesof voltage on electrodes which control the movements of the ions.Because of the application of voltage pulses on the ion-acceleratingeleck trodes, a certain amount of instability has been inherent in theoperation of the time-of-light mass spectrometers. Such instabilityoccurs because it is diicult to produce successive voltage pulses havingthe same amplitude and shape and, therefore, the acceleration providedby each pulse is dilerent. This instability has prevented the full`capabilities of the time-of-flight mass spectrometers from beingrealized to distinguish between the masses ofdiierent ions over a widerange of masses. n

This invention provides a mass spectrometer for producing pulses of ionsby ionizing molecules ofl gas at periodic intervals. The massspectrometer includes vion` accelerating electrodes which` havedirectvvoltages imposed on them to accelerate the ions a moderate amountin a tirst region and a considerable amount in a second region toproduce a separation of the ions on the basis of their mass and acollection of the ions at a focal distance from the regions. By imposingdirect voltages on the electrodes controlling the movements oi the ions,a relatively stable operation is provided in the mass-spectrometer suchthat a relatively sharp .delineation between ions of diierent mass isobtained. Since direct voltages are imposed on the ion-acceleratingelectrodes,.ther eleck trical system forming a part of the massspectrometer is also'considerably simplied. y

An object of this invention is to provide a mass spectrometer fordetermining thev masses of the differenty gases and vapors in an`unknown mixture byrrieasuring'the times required for ions formed fromthe gases-to travel through a predetermined distance.

Another object is to provide a mass spectrometer of the above.characterl for producing pulseslofl ions and for imposing constantforces on the ions `to producela separation of the ions on the basis ofthe masses of the r 2,743,370 Patented Apr. 24, 1956 ICC ions during themovement of the ions through a predeL termined distance. f

A further object is to provide a mass spectrometer of the abovevcharacter which is more stable inv operation than the time-of-ight massspectrometers now Ain use.

Still another object is to provide a mass spectrometer of the abovecharacter requiring the use .of relatively simple electrical componentsto provide a relatively sharp y delineation between ions of differentmass.

A still further robject is tov provide amethod of producing 'pulses ofions and of separating the diiferent ions in each pulse on they basis oftheir mass so as to determine the masses of the ions. v

Other objects and advantages will be apparent from a detaileddescription of the invention and from `the appended drawings and claims.

In'the drawings:

Figure l is a somewhat schematic view, partly in block form and partlyin perspective, illustrating the mechanical and electrical featureswhich together constitute one embodiment of the invention; and f Figure2 is a somewhat schematic view, partly in block form and partly invertical section, illustrating a modi' tication of the invention fordetecting ions of a particu* lar mass. f

In the embodiment of the'invention shown in Figure 1, a lament 10 madefrom a suitable lmaterial such as tungsten is provided. The lament hasthe shape of fa wedge in a substantially vertical plane asseeny inFigure 1 and has a relatively great width, suchas 2.5 centimeters. Acontrol electrode 12 is disposed ata relatively close distance to thefilament `10 and isprovided with av horizontal slot 14 aligned with thetip of the lament 10 along the complete width ofthe filament. 1` Anacceleratingelectrode 16 having .a slotf18 corresponding substantiallyin shape and position tol the slot 14 is positioned in substantiallyparallel relationship with the electrode 12. Theelectrode16isffseparated from the electrode 12 by a relatively smalldistance, such as 2 millimeters. A collector20 is disposed atA amoderate distance, such as 1 or2 centimeters, from the electroder 16andin substantially parallel relationship to the elec'- trode. v l Abacking plate 22 having a relatively restricted length such as 1centimeter is provided at an intermediate'position v'between theelectrode =1`6 and the collector 20. The. backing plate 22 issubstantially perpendicular tothe' electrode 16-and the collector 20 andis slightly to the rear. of an imaginary line extending from the tipoflthe filament 10 through the-'slots 14 and 18 to the collector 20. Acontrol electrode 24 madesfrom a suitable wire mesh is disposed insubstantially parallel relationship to the backingv plate 22 and at arelatively close distance,

such as 2 millimeters, from the backing plate. The elec trode 24is'slightlyin-front of the imaginary line disclosed above. Slats26vextend laterally. from the backingplate 22 to the electrode 24 tofform a compartment with the electrode 16 and thefcollector 20. y

A vertical slot 28 is provided Ain one of the slats 26 at a positionsubstantiallygaligned with the imaginary line' disclosed above. The slot28 communicates with a cond uit 30 which extends from a receptacle y32adapted to hold molecules of the dierent gases or vapors'consti-lelectrode 36 is in turn positioned at a relatively great.r

distance, Vsuch as 40centimeters, from the electrode A34. The electrodeA36 isalso madefrom ra suitable Wire lmesh and is positioned insubstantially parallel relationship to the electrode 34.

A detector is positioned at a moderate distance, such as 3 centimeters,from the electrode.- For example, the detector may constitute acollector 3S or electrony multiplier similar to that disclosed onpage.831 et Radio Engineering" (third edition, 1947)- byV Professorl Fred.erick E. Terman. A time indicator, such as anoscilloscope 40, isconnected to the collector 3S through: amplifiers 41 to indicate therelative times at which. signals are produced by the, collector. Aconnection is also made from the output terminal of ay pulse forming,circuit 42 to ana input terminal of the oscilloscope 40@ so that thesweep of the beam in the oscilloscope will be initiated. everyv timethat a pulseisproduced by the circuit;4 42;

A relatively high positive. voltage, such as 275: volts is applied to;the filament through a. resistance 43 from a suitable power supply 44.Positive voltages in the order of 250 volts and 375 volts are`respectively applied to the electrodes 12 and 16 through suitableresistances 46 and 4S from the power supply 44. A voltage of 375 voltsis also applied to the collector througha resistance 50.

Positive voltages of 400 and3150 `volts are applied to the backing plate22 and the electrode 24 through suitable resistances 52 and` 54,respectively, from the power supply 42. A positive voltage ofapproximately 50. volts is applied to the collector 38 through asuitable resistance 56 so that electrons secondarily emitted from thecollector by the impingement of ions will be attracted back to thecollector, The electrodes 34 and 36. are 4directly grounded.

Since the voltage on the. control electrode 12. is. lower than thevoltage on: the filament 10, electrons emitted by the filament areprevented from moving: past, the electrode 12 into the region betweenthe backing plate. 22 and. the electrode 24. Because of the forceimposed on the electrons to prevent them from. travellinginto the regionbetween the backing plate 22 and the' electrode 24, moleculeso gas orvapor introduced into the region from the receptacle 32V cannot beVionized.

At predetermined times, voltage pulses having a relatively shortdurations such: as4 0.01 microsecond and having a magnitude in the orderof F{-50: volts are applied to the electrode 12. The voltage pulses areapplied to the electrode 12 through a coupling capacitance 58 fromy thepulse forming circuit 42. The pulse forming circuit 42 may be similar tothat disclosed and claimed in co-pendi-ng application Serial No. 230,905filed lune llt, l95l byI William C. Wiley.

Upon the application of each voltage pulse to the electrode 12, thevoltage on the electrode becomes greater than the voltage on thefilament 10. This causes the electrons emitted by the filament to beaccelerated towards the electrode 12. The electrons movingV past theelectrode 12 upon the imposition of a voltage pulse on the electrode arefurther accelerated in the region betweenthe electrodes 12 and 16. Theelectrons are accelerated in this region since the electrode 16 is. a-ta higher potential than the electrode 1-2 even during the time that thevoltage pulse is applied to the electrode 12.

Because of the accelerations imparted to the electrons in the regionbetween the filament 10l and the electrode 12 and in the region between.the electrodes 12 and 16, the electrons have a considerable energyr asthey travel through the region between the backing plate 22 and theelectrode 24. After travelling through this region, the electronsimpinge on the collector 20aY As the electrons move through the regionbetween the backing plate 22 and the electrode 24, some of them strikemolecules of gas introduced into the region from the receptacle 32.Since the electrons have had considerable accelerations imparted to thembetween thegfilament 10 and the electrode 1'6, they strike the. gasmolecules with a suicient force to produce an ionization of themolecules into electrons and positive ions. Most of the ions have asingle positive charge but a few of the ions have more than one chargebecause of a loss of two or more electrons from the gas molecules.

Since the backing plate 22 is at a positive potential with respect tothe voltage on the electrode 24, a repelling force is applied on theions to move them towards the electrode 24. This repelling force is ofonly` moderate magnitude because of the difference of 50 volts betweenthe potentials applied to the backing plate 22 and the electrode 24.This repelling force imparts a greater acceleration to the ions ofrelatively light mass than to the ions of heavy mass. In this way, the.light ions attain a greater speed than the heavy ions.

After the ions have traveled past the electrode 24, they are subjectedto a force which is considerably greater than that imposed on them inthe region between the backing plate 22 and the electrode 24. Such, aconsiderable force is imposed on the ions in the region between theelectrodes 24 and 34 because of the difference. of approximately 35.0volts between, the potentials imposed on the electrodes.

Since the electrodes 34 and 36 are both at substantially groundpotentials, no force is exertedv upon the ions in this region. Thiscauses the ions to travel through the region with substantially the same'velocity as that attained by them as they move past the. electrode 34.After moving past the electrode 36, the ions impinge on the collector 38and produce signals having strengths dependent (in part) upon therelative abundance of the different gases or vapors in the unknownmixture. The signals produced by the collector 38 are amplied by theamplifiers 41 and are visually displayed ou the oscilloscope 40. Bydetermining the relative times at which the signals appear on theoscilloscope, the masses of the different ions can be determined. Therelative abundance of the ions can also be determined from theamplitudes ot the different signals.

The mass spectrometer disclosed above has several important advantages.Since the filament 10 has a considerable width, a relatively largenumber of electrons are accelerated into the region between the backingplate 22 and the electrode 24 during the short period of time that thepulse of voltage is applied to the electrode 12. As a result, arelatively large number ot ions are instantaneously produced by theimpingement of the electrons on molecules of gas introduced into theregion between the backing plate 22 and the electrode 24.

Since the backing plate 22 and the electrode 24 have restricted lengths,they are not able to produce any material deflection of the electronspassing between them. The action of the plate 22 and the electrode 24 indeflecting the electrons from a straight path is further limited becauseof the moderate voltage difference between the plate and the electrode.The deection of the electrons from a straight path is also limitedbecause of the intermediate voltage on the electrode 16 and thecollector 2i) relative to the voltages on the plate 22 and the electrode24.

Since the backing plate 22 and the electrodes 24 and 34 are maintainedat substantially constant potentials, they impart a relatively stableoperation to the spectrometer during the acceleration of the ions in theregion between the backing plate 22 and the electrode 24 and in theregion between the electrodes, 24 and 34. Because of the stableoperation of the mass spectrometer during these periods of ionacceleration, the ions become separated more sharply on the basis of.their mass than in timc-O-flight mass spectrometers operating withvoltage pulses which do not maintain a constant amplitude and shape.This relatively sharp delineation between ions of different mass causesions of adjacent masses to be distinguished from one another over a widerange of values.

The imposition of the particular voltages on the backi'ng plate 22 andthe Velectrodes 24 and 34 provides a compensation for difierences in thepositioning and random maar@ motion, ofthe ions at the instant that theions are formed. 'Ille-differences in the positioning of the ions areproduced because of the finite width of the electron beam. 'Ihe finitewidth of the electron beam is produced because of the collimating actionwhich is provided on the electrons by the slots 14 and 18. Differencesin the random motion of individual ions are caused by the thermal andother energy in the ions. Because-of the differences in the randommotionof the ions, some of the ions `may be travelling towards the plate 22 atthe instant that they are formed from gas molecules and other ions maybe travelling towards the electrode 24. f The compensation for thedierences in the positioning and-random motion of individual ions isprovided because of the moderate acceleration imposed on the ions intheregion between the backing plate 22 and the electrode 24 and theconsiderable acceleration imposed on the ions in the region between theelectrodes -24 and 34. The compensatoryaction provided-on the ions inthese regions lis fully disclosed in co-'pending application Serial No.249,318 tiled October 2, 1951 byrWilliam C. Wiley. Such compensatoryaction is provided even though constant voltages are imposed on thebacking plate 22 and theelectrodes 24 and 34 instead of the pulses ofvoltage disclosed in the co-pending application. j The'r'elatively shorttime of 0.01 microsecond for the flow of electrons through the slots 14and 18 also facilitates the `production of relatively sharp outputsignals. Sharp output signals are produced since the period of 0.01microsecondy is considerably less than the time required for the ions ofeach mass in a pulse to be collected. It has been found that the periodof time required for the ions of each mass in a pulse to be collectedapproximates 0.05.microsecond. The ions of each mass in a pulse arecollected at ay different time from the ions of all other masses inthe'pulse because of the separation of the ions on the basis of theirmass during their travel towards the collector 38. `In the massyspectrometer constituting this invention, a pulse of voltage is appliedonly to the electrode 12. ln-this respect, the mass spectrometerdisclosed above differs from' other time-'of-tlight mass spectrometersnow in Ause. These spectrometers require the vinitial mposition/,ofvoltage pulses on electrodes controlling the movement of the electrons'and the'subsequent imposition of voltage pulses on electrodescontrolling the movement of the ions. Since a voltage pulse is imposedlonly on the electrode 12 in'the mass spectrometer constituting thisinvention, the pulserforming circuitSS shown in block form in Figure lcan be relatively simple. Since a pulse is applied by the pulse forming'circuit 42 only to the electrode 12, the period of time required Vforelectrons to travel'into the region between the backing plate 22 and theelectrode 24 can be arithmetically approximated. The period' oftimerequired for the ions of each mass to travel tothe collector 38 canalso be arithmetically approximated. By adding .together the two periodsof time, ali-approximation can be made oftherelative time between the`formation of a voltage pulse by the circuit 42 and the appearance `onthe voscilloscope 40 of a signal produced byions of a particular mass.

yIn Figure 2, a system is shown for distinguishing between'ions of aparticular mass and all other ions.l 'T he system includes a delaynetwork 80 having an input termi- 'n'al connected'to the output terminalyof the purse forming circuit 42 and having an outputterminal connectedto anfinput terminal of an oscilloscope 32. The network ttloperatesv todelay the pulse produced by the -circuit 42 for 'a period of timecorresponding to that required 4for the ions of the particular mass toreach the collector 38. The network then introduces the pulse to theoscilloscope 82, which operates to provide anindication only during thetime that a pulse is introduced-to it from the network. -Inthisfway, theoscilloscope 82 provides an indication only as to the presence orabsence of ions of a particular 6 mass in eachion pulse. Y whenVthernass spectrometer is utilized withother components to @form a leakdetector since an indication by the oscilloscope 82 ofa particular gas,such as helium` indicates the presence of a leak in the equipment beingtested. t f t f 'Although this invention has been disclosed andillustrated with reference to particular applications, the principlesinvolved are susceptible of numerous other applications which will beapparent to persons skilled in the art. The invention is, therefore, tobe limited only as indicated Aby `the scope of the appended claims.

What is claimedis: t i

l l. A mass spectrometer, including, means for providing a pluralityofelectrons, means forproviding a rst region with the electron means,means 'for imposing on the electrons in ythe fifrsttregion a force ofrelatively long duration to prevent the movement of the electrons fromthe electron providing means, means for imp osing on the electrons `apulsating 'force v.of relatively short duration totaccelerate theelectrons 'through the region, means for` providing a second regiondisposed relative to the first region to form a channel for the passageof electronsgmeans for introducing a plurality of molecules of gas into.the second region for ionization by the electrons passing through theregion, means for, imposing on the ions in the second region ya force ofsubstantially constant magnitude to accelerate the ions through theregion and torproduce a separation of the ions on the basis of theirVmass,'means for detecting the ions after their travel through arelatively great distance past the second region, and means 'forindicating the relative times at which the ions of different mass aredetected.

'2. A mass spectrometer, including, means for providing a plurality ofelectrons, means for providing a first region with the electron means,means for imposing on the electrons in the `first region an electricalfield to restrain the movement ofthe electrons from the emitting means,means for imposing'yon the electrons in the first region an lelectricalfield of'relatively short duration to accelerate the electrons throughthe region, means rfor providing a second region in a direction disposedto provide a channel for the passage of electrons through theregion,means for introducingla plurality of molecules of gas into the.second regionl for ionization by the electrons, passing vthrough theregion, means lfor imposing anelectrical field of substantially constantmagnitude on Vthe. ions in the 'second region to produce an accelerationof 4the ions through the regionfand a separation vof the ions onthebasis of their mass, means for detecting the ions-after their travelthrough afrelatively great dis-V tance past the second region, and meansfor indicating the relative tirnes'at which the ions of different massare detected.

31A mass/spectrometer', including, av filament for emitting a pluralityof electrons, a control electrode separated from the filament by arrelatively short distance, means for applying direct voltages on thelame'ntrand the electrode of such magnitude as to produce yan electricfield between them for preventing the flow of electrons towards theelectrode, means for applying pulses of voltage between the filament andthe electrode to produce a flow of electrons past the electrode duringthe pulses, a collector for receiving the electrons flowing past theelectrode, a backing plate disposed between the control electrode andthe collector and in substantially the same direction as the-electronflow, anion electrode separated from the backing plate by arelativelyshort distance and defining with the yplate a region through whichthe'electrons low, means for introducing into the region between thebacking plate and the ion electrode a plurality of gas molecules forionization by the electrons, means for applying 'direct vvoltages onlthe backing plate and the ion electrode of suchma'gnitude as to produceany .Such an indication isii'nportant'` produced from the gas molecules,a detector separated from the ion electrode by a relatively greatdistance to receive the ions, and a time indicator for determining therelative times at which ions of different mass are detected.

4. A mass spectrometer, including,` a filament for emitting a pluralityof electrons, a rst electrode separated from the iilament by arelatively small distance and having a direct voltage applied to it ofless magnitude than that applied to the filament, a second electrodesepa rated from the first electrode by a relatively small distance andhaving a direct voltage applied to it of greater magnitude than thatapplied to the lilarnent, means for applying a pulse of voltage'to thefirst electrode to bring the voltage on the electrode to an intermediate'magnitude relative to the voltages on` the filament and secondelectrode, a collector for receiving the electrons flowing to it uponthe application of the voltage pulse on the rst electrode, a backingplate disposed between the second electrode and the collector and havinga direct voltage applied to it, an ion electrode separated from thebacking plate by a relatively small distance to define 'ith the plate aregion through which the electrons flow, means for introducing moleculesof gas into the region between the backing plate and the ion electrodefor ionization by the electrons, the ion electrode having a directvoltage applied to it of such magnitude relative to the voltage on thebacking plate as to produce a movement of the ions towards it, adetector separated from the ion electrode by a relatively great distanceto receive the ions, and a time indicator for determining the relativetimes at which the ions of diterent mass are detected.

5. A mass spectrometer, including, a filament for emitting a pluralityof electrons, a iirst electrode disposed at a relatively short distancefrom the filament, means for applying voltages of substantially constantmagnitude on the filament and the electrode to restrain the electronsfrom movement towards the electrode, means for applying pulses ofvoltage on the electrode relative to the voltage on the iilament toaccelerate the electrons towards the electrode, a backing plate disposedin substantially parallel relationship to the direction of electron iiowat a position past the electrode, a secondelectrode disposed insubstantially parallel relationship to the backing plate at a relativelyshort distance from the plate and on the opposite side of the electronflow from the backing plate, means for introducing a plurality of gasmolecules into the region between the backing plate and the secondelectrode for ionization by the electrons, means for applying voltagesof substantially constant magnitude on the backing plate and the secondelectrode to accelerate the ions towards the electrode and to produce aseparation of the ions on the basis of their mass, a detcctor disposedto produce signals in accordance with the time required for the ions ofdifferent mass to travel through a relatively great distance past thesecond electrode, and an indicator for showing the relative times atwhich the different signals are produced by the detector.

6. A mass spectrometer, including, a vfilament for emitting a pluralityof electrons, a first electrode disposed at a relatively short distancefrom the lilament, means for applying voltages of relatively longduration on the filament and the electrode to prevent the movement ofthe electrons towards the electrode, means for applying pulses ofvoltage of relatively short duration on the electrode relative to thevoltage on the filament to accelerate the electrons towards theelectrode, a backing plate, a second electrode disposed at a relativelyshort distance from the backing plate and in substantially parallelrelationship to the backing plate to form a region through which theelectrons flow, means for introducing a plurality of molecules of gas,irito the region between the backing plate and the second electrode forionization of the molecules by the electrons, means for applyingvoltages: ofA substantially constant magnitude on the backing plate andthe second electrode to accelerate the ions towards the electrode and toproduce a separation of the ions on the basis of their mass, means fordetecting the ions after their travel through a relatively greatdistance past the second electrode, and means for indicating therelative times at which the ions of different mass are detected.

7. A mass spectrometer, including, a filament for providing a pluralityof electrons, a collector, means for providing an electric fieldadjacent to the filament for normally restraining the movement ofelectrons towards the collector, means tor varying the electric field inpulses to produce a movement of the electrons towards the collector, abacking plate, an electrode separated from the plate by a relativelyshort distance, the backing plate and the electrode being disposedrelative to the electron flow to pro vide for the passage of theelectrons between the plate and the eleetrode,means for introducing aplurality of molecules of different gas into the region between thebacking plate and the electrode for ionization by the electrons, a powersupply for applying direct voltages to the backing plate and theelectrode of such magnitude as to produce an acceleration of the ionstowards the electrode and a sepa ration of the ions on the basis oftheir mass, a detector located at a relatively great distance past theelectrode in the direction of ion travel to produce signals dependentupon the times at which the ions of dilierent mass travel through thedistance, and an indicator` for showing the relative times at which thedilerent signals are produced by the detector.

8. A mass spectrometer, including, a filament shaped to emit a beam ofelectrons having a relatively large dimension in a transverse direction,a iirst electrode disposed at a relatively close distance to the lamentand in substantially parallel relationship to the filament in thetransverse direction of the electron beam, means for applying directvoltages on the lament and the electrode of such magnitude as torestrain the flow of electrons towards the electrode, a pulse formingcircuit for applying pulses of voltage on the electrode relative to thevoltage on the lament to accelerate the electrons towards the electrode,a backing plate disposed in substantially parallel relationship to thedirection of electron travel, a second electrode disposed insubstantially parallel relationship to the backing plate at a relativelyclose distance to the plate and on the far side of the electron flowfrom the backing plate, means for introducing a plurality of moleculesof gas into the region between the backing plate and the secondelectrode to obtain an ionization of the molecules by the electronsowing through the region, ages on the backing plate and the secondelectrode of such magnitude as to produce a movement of the ions towardsthe electrode and a separation of the ions on the basis of their mass, adetector for producing signals at times corresponding to those requiredfor the ions of different mass to travel through a predetermined andrelatively great distance past the second electrode, and an indicatorfor determining the relative times at which the signals are produced bythe detector.

9. A mass spectrometer including, means for providing a plurality ofelectrons, means for providing a rst region, means for normallypreventingr a movement of the electrons through the region, means forintroducing a plurality of molecules into the rst region, means forimparting an instantaneous pulse of energy to the electrons to produce amovement of the electrons through the region for ionization of differentmolecules introduced into the region, means for providing asubstantially constant electrical eld in the iirst region for a movementof the ions through the region and a separation of the ions on the basisof their mass, means for detecting the ions after their travel through aparticular distance past the first region in accordance with the timerequired for the ions to travel through the distance, and means forindicating the relative times at which the ions of dierent mass aredetected.

l0. A mass spectrometer including, a filament for emitmeans for applyingdirect voltt ting a plurality of electrons, a rst electrode disposed ata particular distance from the filament, an electrical circuit forapplying a voltage on the electrode relative to the voltage on thefilament to prevent the movement of electrons past the electrode, anelectrical circuit for applying an instantaneous pulse of voltage on theelectrode relative to the voltage on the filament to produce a movementof the electrons past the electrode, a backing plate disposed in adirection transverse to the movement of electrons, a second electrodeseparated from the backing plate by a particular distance to define withthe lplate a region through which the electrons flow upon their movementpast the first electrode, means for introducing molecules into theregion between the backing plate and the second electrode for ionizationby the electrons, an electrical circuit for applying a substantiallyconstant voltage difference between the backing plate and the secondelectrode to produce an electrical field for the movement of the ionstowards the electrode and a separation of the ions on the basis of theirmass, a detector disposed at a particular distance past the secondelectrode to produce signals in accordance with the time required forthe diierent ions to travel through the particular distance, andv anindicator for indicating the signals produced by the detector.

1l. A mass spectrometer including, a backing plate, a first electrodealigned with the backing plate at a particular distance from the plate,means for introducing a plurality of molecules into the region betweenthe backing plate and the first electrode, means for providing aplurality of electrons, a second electrode disposed in the path of theelectron tiow, an electrical circuit for biasing the electrode toprevent the iiow of electrons through the region between the backingplate and the first electrode, an electrical circuit for applyinginstantaneous pulses of voltage to the second electrode to produce amovement of the electrons through the region between the backing plateand the first electrode for an ionization of molecules introduced intothe region, electrical means for producing a substantially constantelectrical iield in the region between the backing plate and the firstelectrode for a movement of the ions through the region and a separationof the ions on the basis of their mass, a detector disposed at aparticular distance from the rst electrode to produce signals upon themovement of the ions through the distance, and an indicator forindicating the different signals produced at the detector.

12. A mass spectrometer, including, means for providing a first region,means for providing a plurality of electrons, means for imposing asubstantially constant force on the electrons to prevent the electronsfrom moving through the first region, means for introducing a pluralityof molecules into the first region, means for imposing a force of arelatively short duration on the electrons to produce a movement ofelectrons through the first region for ionization of the molecules,means for imposing a substantially constant electrical force in thefirst region to produce a movement of the ions through the first regionand a separation of the ions on the basis of their mass, a detectordisposed at a particular distance past the rst region to produce signalsupon the movement of the ions through the region, and means forindicating the dilierent signals produced at the detector.

13. VA mass spectrometer, including, a filament for emitting a pluralityof electrons, a first electrode disposed at a particular distance fromthe filament, an electrical circuit for normally applying a voltage onthe electrode relative to the voltage on the filament to restrain theelectrons from movement towards the electrode, a pulse forming circuitfor applying pulses of voltage on the electrode relative to the voltageon the filament to provide the electrons with energy for movement pastthe electrode, a backing plate disposed in substantially parallelrelationship to the electrode at a position past the electrode and onone side of the electron flow, a second electrode disposed insubstantially parallel relationship to the backing plate at a particulardistance from the plate and on the opposite side of the electron ow fromthe backing plate, means for introducing a plurality of molecules intothe region between the backing plate and the second electrode forionization by the electrons, an electrical circuit for applying betweenthe backing plate and the second electrode a relatively constant voltagediiierence of a polarity to produce a movement of the ions towards theelectrode and a separation of the ions on the basis of their mass,

a detector disposed at a particular distance past the sec? ond electrodeto produce signals in accordance with the time required for the ions ofdifferent mass to travel through the particular distance, and anindicator for indicating the detection of the ions of different mass.

UNITED STATES PATENTS References Cited in the tile of this patent

